This invention relates to the field of blast treatment devices. More particularly, it relates to that class of devices which are capable of blast treatment by projecting particulate at high velocity against a part to be cleaned, deburred or otherwise treated. Typically this blast treatment is accomplished by the use of centrifugal throwing wheels which receive particulate at the center of the wheel and project it outwardly by use of a series of radially positioned blades. In the usual application the projected particulate causes wear on the surface of the blades which are replaceable at service intervals. This normal situation obtains when a control cage is employed for directing the blast in a particular direction to strike a target.
Recently it has become desirable to alter the construction and operation of the device somewhat to obtain certain objectives. In order to scrub sand used in foundry operations, it is often desirable to project the sand against a target and have it rebound therefrom through a stream of oncoming particles to, in effect, scrub the surface of the sand grains. This frees the sand of foundry binder and reduces the cost of the molding operation. When a blast wheel is used for this purpose it is used without a direction control cage and is referred to as a bare wheel assembly. Bare wheel assemblies utilize relatively high R.P.M. motors to maximize the scrubbing effect on the abrasive or sand being treated.
A particular problem which arises when a bare wheel assembly is utilized for blast treatment or sand srubbing is the heavy wear which occurs on the spacer elements provided in the standard blast wheel. Spacer elements are generally provided behind each blade in the wheel and, depending upon the design, serve one or more functions as follows. The blades are generally mounted in the wheel positioned between a front and back plate. The front and back plate are fastened to spacers. The side plates are spaced so that the blades may be removed when necessary without otherwise disassembling the wheel. In some constructions the spacers serve the additional purpose of securing the blade in the desired radial position. Exemplary of blades in which spacers are employed are the devices disclosed in U.S. Pat. Nos. 3,683,556 and 3,785,105.
As mentioned, when a bare wheel assembly is employed, that is, a wheel without a control cage, the particulate thrown travels in all directions and a portion of the particulate impinges upon the spacers causing them to wear excessively.
According to the present invention bare wheel assemblies are disclosed which eliminate the need for spacers and thereby obviates the problem of excess wear on those elements.
It is accordingly an object of the present invention to provide an improved blast wheel design which securely locks the throwing blades into a blast wheel without the use of spacers.
Another object of the invention is to provide an improved spacerless blast wheel which securely positions the throwing blades in the wheel.
Another object of the invention is to provide a blast wheel capable of securing blades to one side of the wheel in a desired angular orientation.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.